Xinxin Lu

A study of 239Pu production rate in a water cooled natural uranium blanket mock-up of a fusion–fission hybrid reactor

The 239Pu production rate is important data in neutronics design for a natural uranium blanket of a fusion–fission hybrid reactor, and the accuracy and reliability should be validated by integral experiments. The distribution of 239Pu production rates in a subcritical natural uranium blanket mock-up was obtained for the first time with a D-T neutron generator by using an activation technique. Natural uranium foils were placed in different spatial locations of the mock-up, the counts of 277.6 keV γ-rays emitted from 239Np generated by 238U capture reaction were measured by an HPGe γ spectrometer, and the self-absorption of natural uranium foils was corrected. The experiment was analyzed using the Super Monte Carlo neutron transport code SuperMC2.0 with recent nuclear data of 238U from the ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0u2, JEFF-3.2 and CENDL-3.1 libraries. Calculation results with the JEFF-3.2 library agree with the experimental ones best, and they agree within the experimental uncertainty in general with the average ratios of calculation results to experimental results (C/E) in the range of 0.93 to 1.01.

Measurement and analysis of fission rates in depleted uranium and depleted uranium–polyethylene shells with neutrons from D-T reaction

To validate the concept design of a novel fusion–fission hybrid energy reactor, a depleted uranium assembly and a combined assembly of uranium and polyethylene were designed and assembled based on a depleted uranium spherical shell and a polyethylene spherical shell. The distribution of the fission rates for the depleted uranium and enriched uranium in the two assemblies, as a function of the distance of the detection position to the centre, was measured using a plate fission chamber bombarded by D-T neutrons. The addition of a polyethylene shell significantly changed the neutron spectrum; in particular, the neutron fluxes with energies of 1 MeV and lower were changed. Using MCNP5 and the attached libraries, the fission rate experiments were simulated, and the experimental configuration, including the wall of the experimental hall, was described in detail in the model. The fission rate distributions for depleted uranium and enriched uranium in the two assemblies were reproducible. The difference between the calculated results with different libraries and different tallies is as small as 1.0%. By considering the neutron flux, the fission rate and the C/E values, it is concluded that the fission rates of depleted uranium and enriched uranium induced by the fast neutrons were overestimated, and it is proposed that the fission parameters of uranium for fast neutrons should be re-evaluated, or the margin of the concept design should be enlarged, to make the concept effective.